The present invention relates to sensor apparatus for measuring the rotation rate of a rotating shaft, such as a turbine engine shaft.
One type of conventional turbine shaft tachometer employs a magnetic pick-up on the turbine blade to electrically induce a voltage which is proportional to rotation speed. Another type of turbine shaft tachometer uses a gear ratio pick-up off the drive train to mechanically gear down the shaft rotation speed. These methods work but suffer from extreme temperatures, electromagnetic interference and large angular noise spectral density due to engine action and gear backlash. These three factors can induce high sensor failure rate and require expensive schemes in packaging to insure survivability. Moreover, these methods are neither very accurate, very fast, or immune to electromagnetic interference.